A 5G communications system is dedicated to supporting higher system performance and supports a plurality of service types, different deployment scenarios, and a wider frequency spectrum scope. The plurality of service types includes enhanced mobile broadband (eMBB), massive machine type communications (mMTC), ultra-reliable and low latency communications (URLLC), a Multimedia Broadcast Multicast Service (MBMS), and a positioning service. The different deployment scenarios include an indoor hotspot scenario, a dense urban scenario, a suburb scenario, an urban macro cell, a high-speed rail scenario, and the like.
A major feature of the 5G communications system relative to a 4G communications system is that support for an ultra-reliable and low latency communications (URLLC) service is added. There is a plurality of URLLC service types, and examples include industrial control, industrial production process automation, man-machine interaction, telemedicine, and the like. Primary indicator requirements of a URLLC service include latency and reliability.
A typical requirement of the URLLC service for a latency on a user plane is 0.5 ms for both uplink and downlink, and a typical requirement for reliability is to reach 99.999% reliability within 1 ms. It should be noted that the foregoing performance indicators are merely typical values. A specific URLLC service may have a different requirement for reliability. For example, extremely stringent industrial control requires an end-to-end latency of 0.25 ms or less and a transmission success probability of 99.9999999%.
A current basic scheduling policy of a URLLC service may be classified into two types. One is a one-time transmission mode in which error correction does not depend on feedback and data retransmission. This requires allocation of adequate time-frequency resources in first-time data transmission to ensure reliability of one-time transmission. A resource utilization rate of this scheduling policy is relatively low. The other scheduling policy is a feedback-based automatic repeat mode in which data reliability can be ensured by performing transmission a plurality of times in a range allowed by a latency. Resource utilization of this scheduling policy is obviously higher than that of the first policy, but a latency of this scheduling policy is greater than that of the first policy.
In different URLLC service scenarios, reliability and latency requirements are different. In existing wireless communications technologies, service data is generally transmitted using a fixed transmission mode, making it difficult to meet flexible reliability and latency requirements in the URLLC service scenarios.